Automatic Gain Control for Capacitive Touch Panel Sensing System

ABSTRACT

Disclosed are capacitive touchscreen or touch panel systems, devices and methods which increase the dynamic range of touches that may be detected on a capacitive touch screen or touch panel. Increased dynamic range is provided by employing automatic gain control methodologies and circuitry to process signals corresponding to individual mutual capacitance cells in a touch screen or touch panel.

FIELD

Various embodiments described herein relate to the field of touchscreenor touchpad systems, devices, components and methods configured todetect touches on a touchscreen or touch panel using capacitive sensingtechniques.

BACKGROUND

Capacitive touch panel sensors include touchscreens or touch panelscomprising arrays of sensing cells. Touches cause capacitance change atthe cell or cells underlying the region being touched. The touchscreencontroller detects and locates the capacitance changes by analyzingsignals generated by the cells due to capacitance change, the signalsundergoing analog amplification and filtering followed by digitizationand subsequent digital signal processing. The primary result of theanalysis is the determination of the affected cell position and hence,the corresponding touch location.

However, the cells in any given array may vary widely in theircapacitance values. This intrinsic variation, combined with variation inthe characteristics of analog amplification components, power supplyvariations and other factors can cause the signal amplitudes output bythe cells to vary through a dynamic range of up to 20 dB. Such a largevariation complicates the determination of touch position. Approachessuch as applying a global signal threshold to distinguish between touchand no-touch states have been discovered to be of limited value.

What is needed is a touchscreen system, and method of operating such asystem, that can equalize the effective gain of each individual cell ofa touch panel sensor without causing deterioration in the sensor'sability to track touches of interest.

SUMMARY

According to one embodiment, there is provided a capacitive touchscreenor touch panel system comprising a touchscreen comprising a firstplurality of electrically conductive drive electrodes arranged in rowsor columns, and a second plurality of electrically conductive senseelectrodes arranged in rows or columns arranged at an angle with respectto the rows or columns of the first plurality of electrodes, mutualcapacitances existing between the first and second pluralities ofelectrodes at locations where the first and second pluralities ofelectrodes intersect to form individual cells, the mutual capacitanceschanging in the presence of one or more fingers of a user or touchdevices brought into proximity thereto, drive circuitry operablyconnected to the first plurality of drive electrodes, sense circuitryoperably connected to the second plurality of sense electrodes andconfigured to sense input signals corresponding to the individual cellstherefrom, and a controller operably connected to the first plurality ofdrive electrodes and the second plurality of sense electrodes, thecontroller comprising a central processing unit (CPU) and automaticlevel control (ALC) circuitry comprising at least one scaler anddecimator circuit configured to receive signals corresponding to theindividual cells and to provide therefrom scaled and decimated outputsignals corresponding to such individual cells, a multiplier circuitoperably connected to the scaler and decimator circuit and configured toreceive the scaled and decimated output signals therefrom, and furtherto multiply such scaled and decimated output signals by a gain factorand to provide multiplier output signals therefrom, a first subtractorcircuit operably connected to the multiplier circuit and configured toreceive the multiplier output signals therefrom and to subtract apredetermined set point value from such multiplier output signalsthereby to provide error output signals therefrom, an ALC control loopfilter circuit operably connected to the CPU and the multiplier circuitand configured to calculate updated gain factors based on the erroroutput signals and to provide such updated gain factors to themultiplier circuit, and a second subtractor circuit configured tosubtract multiplied output signals from a desired set point value and toprovide final output signals corresponding thereto to the CPU, whereinthe CPU is configured to calculate touch position data based on thefinal output signals corresponding to the positions of the one or morefingers of the user or touch devices.

According to another embodiment, there is provided method of detectingtouches on a capacitive touchscreen or touch panel system, the systemcomprising a touchscreen comprising a first plurality of electricallyconductive drive electrodes arranged in rows or columns, and a secondplurality of electrically conductive sense electrodes arranged in rowsor columns arranged at an angle with respect to the rows or columns ofthe first plurality of electrodes, mutual capacitances existing betweenthe first and second pluralities of electrodes at locations where thefirst and second pluralities of electrodes intersect to form individualcells, the mutual capacitances changing in the presence of one or morefingers of a user or touch devices brought into proximity thereto, drivecircuitry operably connected to the first plurality of drive electrodes,sense circuitry operably connected to the second plurality of senseelectrodes and configured to sense input signals corresponding to theindividual cells therefrom, and a controller operably connected to thefirst plurality of drive electrodes and the second plurality of senseelectrodes, the controller comprising a central processing unit (CPU)and automatic level control (ALC) circuitry, the method comprisingscaling and decimating signals corresponding to the individual cells toprovide scaled and decimated output signals corresponding to theindividual cells, multiplying the scaled and decimated output signals bya gain factor to provide multiplied output signals, subtracting themultiplied output signals from a predetermined set point value toprovide error output signals, calculating updated gain factors based onthe error output signals, subtracting multiplied output signals from adesired set point value and providing final output signals correspondingthereto, and calculating touch position data based on the final outputsignals that correspond to the positions of the one or more fingers ofthe user or touch devices.

Further embodiments are disclosed herein or will become apparent tothose skilled in the art after having read and understood thespecification and drawings hereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Different aspects of the various embodiments will become apparent fromthe following specification, drawings and claims in which:

FIG. 1 shows a cross-sectional view of one embodiment of a capacitivetouchscreen system;

FIG. 2 shows a block diagram of a capacitive touchscreen controller;

FIG. 3 shows one embodiment of a block diagram of a capacitivetouchscreen system and a host controller;

FIG. 4 shows a schematic block diagram of one embodiment of a capacitivetouchscreen system;

FIG. 5 shows a schematic block diagram of one embodiment of atouchscreen system including automatic gain control;

FIG. 6 shows a schematic block diagram of one embodiment of a touchscreen controller;

FIG. 7 shows a flowchart for one embodiment of a method for controllinga touchscreen system that employs automatic gain control.

The drawings are not necessarily to scale. Like numbers refer to likeparts or steps throughout the drawings.

DETAILED DESCRIPTIONS OF SOME EMBODIMENTS

As illustrated in FIG. 1, a capacitive touchscreen system 110 typicallyconsists of an underlying LCD or OLED display 112, an overlyingtouch-sensitive panel or touchscreen 90, a protective cover ordielectric plate 95 disposed over the touchscreen 90, and a touchscreencontroller, micro-processor, application specific integrated circuit(“ASIC”) or CPU 100. Note that image displays other than LCDs or OLEDsmay be disposed beneath touchscreen 90.

FIG. 2 shows a block diagram of one embodiment of a touchscreencontroller 100. In one embodiment, touchscreen controller 100 may be anAvago Technologies™ AMRI-5000 ASIC or chip 100 modified in accordancewith the teachings presented herein. In one embodiment, touchscreencontroller is a low-power capacitive touch-panel controller designed toprovide a touchscreen system with high-accuracy, on-screen navigation.

Capacitive touchscreens or touch panels 90 shown in FIGS. 3 and 4 can beformed by applying a conductive material such as Indium Tin Oxide (ITO)to the surface(s) of a dielectric plate, which typically comprisesglass, plastic or another suitable electrically insulative andpreferably optically transmissive material, and which is usuallyconfigured in the shape of an electrode grid. The capacitance of thegrid holds an electrical charge, and touching the panel with a fingerpresents a circuit path to the user's body, which causes a change in thecapacitance.

Touchscreen controller 100 senses and analyzes the coordinates of thesechanges in capacitance. When touchscreen 90 is affixed to a display witha graphical user interface, on-screen navigation is possible by trackingthe touch coordinates. Often it is necessary to detect multiple touches.The size of the grid is driven by the desired resolution of the touches.Typically there is an additional cover plate 95 to protect the top ITOlayer of touchscreen 90 to form a complete touch screen solution (see,e.g., FIG. 1).

One way to create a touchscreen 90 is to apply an ITO grid on one sideonly of a dielectric plate or substrate. When the touchscreen 90 ismated with a display there is no need for an additional protectivecover. This has the benefit of creating a thinner display system withimproved transmissivity (>90%), enabling brighter and lighter handhelddevices. Applications for touchscreen controller 100 include, but arenot limited to, smart phones, portable media players, mobile internetdevices (MIDs), and GPS devices.

Referring now to FIGS. 3 and 4, in one embodiment the touchscreencontroller 100 includes an analog front end with 9 drive signal linesand 16 sense lines connected to an ITO grid on a touchscreen.Touchscreen controller 100 applies an excitation such as a square wave,meander signal or other suitable type of drive signal to the driveelectrodes that may have a frequency selected from a range between about40 kHz and about 200 kHz. The AC signal is coupled to the sense linesvia mutual capacitance. Touching touchscreen or touch panel 90 with afinger alters the capacitance at the location of the touch. Touchscreencontroller 100 can resolve and track multiple touches simultaneously. Ahigh refresh rate allows the host to track rapid touches and anyadditional movements without appreciable delay. The embedded processorfilters the data, identifies the touch coordinates and reports them tothe host. The embedded firmware can be updated via patch loading. Othernumbers of drive and sense lines are of course contemplated, such as8×12 and 12×20 arrays.

Touchscreen controller 100 may feature multiple operating modes withvarying levels of power consumption. For example, in rest modecontroller 100 may periodically look for touches at a rate programmed bythe rest rate registers. There are multiple rest modes, each withsuccessively lower power consumption. In the absence of a touch for acertain interval controller 100 may automatically shift to thenext-lowest power consumption mode. However, as power consumption isreduced the response time to touches may increases.

According to one embodiment, and as shown in FIG. 4, an ITO grid orother electrode configuration on touchscreen 90 comprises sense columns20 a-20 p and drive rows 10 a-10 i, where sense columns 20 a-20 p areoperably connected to corresponding sense circuits and rows 10 a-10 iare operably connected to corresponding drive circuits. Oneconfiguration for routing ITO or other lines from drive and senseelectrodes to lines to touchscreen controller 100 is shown in FIG. 4.

Those skilled in the art will understand that touchscreen controllers,micro-processors, ASICs or CPUs other than a modified AMRI-5000 chip ortouchscreen controller 100 may be employed in touchscreen system 110,and that different numbers of drive and sense lines, and differentnumbers and configurations of drive and sense electrodes, other thanthose explicitly shown herein may be employed without departing from thescope or spirit of the various embodiments disclosed herein.

FIG. 5 shows a schematic diagram of one embodiment of a touchscreensystem 110 designed to minimize the effect of cell-to-cell variationusing automatic level control (ALC) circuitry 282. Each ALC circuit 282adaptively adjusts the gain of a corresponding individual cell of thetouch panel sensor, with the effect that the cell outputs across thearray are leveled out to have the same “no touch” value.

The signal input from each of the N capacitive cells of the sensorpanel, where N is typically of the order of hundreds or thousands ofcells, is received by scaler and decimator stage or circuit 310 of acorresponding ALC circuit 282. Stage 310 scales and decimates (reducesthe sample rate for) the input signal. The scale factor and decimationfactors are implementation dependent and set the final sample accuracyand maximum bandwidth. The next stage of ALC 282 is a multiplier 315that controls the gain of the cell signal. This constitutes the “plant”in an integral control loop.

The output of multiplier circuit 315 proceeds along two separate paths.One path is the control loop path passing through elements 320, 325 andback to 315. The other path passes through subtractor 330.

Control Loop Path

The control loop calculates an error signal defined as the differencebetween the “Plant Output” (the output of multiplier 282, fed into anegative port of element 320) and a “Desired Set Point” (applied to thepositive port of element 320) as follows:

Error=Desired Set-point−Plant Output  (1)

where the Desired Set Point is a fixed number that represents thedesired plant output for cells that are not being touched.

The error output signal calculated by element 320 as described byequation (1) is fed to ALC control loop filter circuit 325, whichincludes an integrator with controllable front-end gain. The errorsignal is gain-controlled by using a shift register in front of theintegrator. If smaller gains are applied to the error signal, narrowerloop bandwidth results, with correspondingly longer adaptation timeconstants. The loop gain is controlled by firmware (associated with CPU284). The output of the integrator within 325 is fed back to multipliercircuit 315 to control the plant gain. Negative feedback drives theplant gain in the direction that minimizes the error signal.

The control loop filter circuit may be configured to operate in eitherof two modes, which are characterized by long and short time constantsrespectively, and which correspond to slow and fast operation, with lowand high loop bandwidths. System controller 100 acting through CPU 284configures the filter to have a long time constant when the systemfirmware detects a touch, indicated by the cell capacitance signaldropping below a predetermined threshold. The long time constant (lowloop bandwidth) is required so that the finger touch does not get“tracked out” by the ALC if the user's finger remains in contact withthe sensor for several seconds.

System controller 100 acting through CPU 284 configures the filter tohave a short time constant when no touch is detected. This permits rapidadjustment to assure proper trim of the “no-touch” signal gain. Accurateno-touch gain trim allows all cells to have the same effective gain, andcontroller 100 to use the same threshold value for all cells to achieveprecise touch detection.

Subtractor Path

The subtractor stage removes the set-point offset in the signal outputfrom multiplier 315 as shown in equation (2):

Delta Output=Set-point—Plant Output  (2)

The calculated Delta Output normally rests at zero when no touches aredetected. If the delta output is positive, that positive value iscompared with a threshold value to determine if touch contact at thecorresponding cell position can be assumed.

The Delta Output itself can be compensated for gain variations by atable look-up method. This may be particularly useful for panels withvariable thickness covers, causing the delta signal to be lower forcells under thicker sections of panel. The table look-up can beperformed in hardware or firmware. The contents of the table aredetermined by the characteristics of panel 90, and this process is openloop controlled.

Touch controller CPU 284 and associated firmware perform ALCinitialization, ALC loop bandwidth adjustment, touch thresholddetection, and, optionally, delta gain compensation. Controller CPU 284finally outputs the determined touch navigation data of interest to ahost processor.

FIG. 6 shows a schematic diagram of one embodiment of a touch screencontroller ASIC 100 with a touchscreen or touch panel matrix 90 using240 touch cells arranged in a grid of 12×20 cells.

A typical mutual-capacitance measurement technique senses capacitivechanges on the touch panel matrix or touchscreen 90 by measuring thecapacitive coupling between the driver signals, supplied by square waveburst generators 240 through column drivers 250, and the correspondingsignals output from the sense Integrating Programmable Gain Amplifier(IPGA) pins shown on the right hand side of touch panel matrix 90. Itshould be noted that although only one generator 240 and one driver 250are shown explicitly in the figure, other configurations are alsocontemplated, such as one for each column or row of the array. Thesensed signals are amplified and high pass filtered by amplifierelements 255 controlled by coarse gain and analog filter controlelements 260. The gain-adjusted, high-pass-filtered signals arelow-pass-filtered by analog filters 265, and then digitized byconfigurable ADCs 270 before they are filtered by FIR band pass filters272 and down-converted by complex baseband down-converters 274.Down-converters 274 output parallel I and Q data streams, which are fedfirst into FIR low pass filters 276 and then into configurable digitalfilter modules 278.

Outputs from the configurable digital filter modules 278 are filtered byone pole IIR low pass filters 280 and leveled by passage through ALCsautomatic level control circuits 282 before being input to ARM coreprocessor 284. Outputs from the configurable digital filter modules 278also pass through SNR and statistics calculator 288 before reachingprocessor 284.

Navigation-related processing is then carried out by the combination ofCPU or ARM core processor 284 and algorithm coprocessor 286, providinghaptic outputs from haptic driver 290 to host controller 120, andexchanging SPI or TWI data through I2C and SPC driver/receiver interface292 with host controller 120.

It should be noted that although only one each of amplifier element 255,control element 260, low-pass filter 265, ADC 270, FIR BPF 272,down-converter 274, FIR low pass filter 276, digital filter module 278,IIR low pass filter 280, ALC circuit 282 and CPU 284 are shown, otherconfigurations of such and other components are contemplated, such asone set for each row or column of array 90.

In the specific embodiment shown in FIG. 6, there is one IIR low passfilter 280 and one ALC circuit 282 for each of the two hundred and fortycells of array 90, those cells being arranged in a grid of 12×20. Thecapacitors are scanned using 20 row drivers and 12 sense amplifiers.Each cell appears as a capacitor with a nominal value of 2 pF thatreduces in value when touched to around 1.8 pF. Each signal determinedby that capacitance value is sampled and processed so that it ispresented to ALC circuit 282 as a digital value in the range of 5000 to50000.

ALC circuit 282 uses a feedback control loop to normalize the signalrepresenting cell capacitance with respect to a numerical value of16384. There are 240 such ALC loops, one for each cell. The value of16384 is arbitrary and represents the set-point of the control loopcorresponding with a cell that is not touched. Since only changes incapacitance are of interest, the final output is obtained by subtractingthe touch signal from 16384 to create a positive delta value when a cellis touched, that touch causing the capacitance value to be significantlyreduced from its untouched state. Delta values range from 2000 to 5000when a cell is touched, depending on panel and finger characteristics. Athreshold is set by firmware to establish when a touch has occurred.

The integral control loop implementing ALC operation may be clocked indiscrete time intervals, with the filtered touch cell signal beingsampled on each clock interval. In one particular implementation oftouch screen controller ASIC 100 shown in FIG. 6, the firmwareadjustable clock rate is nominally 150 Hz. The input samples are 16 bitunsigned twos complement numbers. These numbers correspond to touch cellcapacitance values. ALC 282 contains a 29 bit integrator register thatcontains the gain value. This number is multiplied by the 16 bit inputto gain control the input. According to one embodiment, the governingequations for a specific implementation are as follows:

cellError=16384−floor(cellIIRout[t]*cellIntegrator[t−1]/33554432)  (3)

cellIntegrator[t]=cellIntegrator[t−1]+floor(cellError*33554432/Ki)  (4)

where Ki=2̂k1 for cellError>0, and Ki=2̂k2 for cellError<0

and k1 and k2 range from 10, 11, 12, . . . 25

cellDeltaOut[t]=floor((cellDeltaCal/4096)*(16384−floor(cellIIRout[t]*cellIntegrator[t]/33554432)))  (5)

where:

-   -   cellIntegrator: 29 bit unsigned integer, 1 of 240 (firmware R/W        and freeze)    -   cellIIRout: 16 bit unsigned integer output of IIR filter, 1 of        240    -   Ki: integration loop gain, based on k1 and k2    -   k1: 5 bit unsigned integer touch loop gain exponent global        variable (firmware R/W)    -   k2: 5 bit unsigned integer anti-touch gain exponent global        variable (firmware R/W)    -   cellDeltaCal: 16 bit unsigned integer, default value is 4096 for        unity gain, 1 of 240 (firmware R/W)    -   cellDeltaOut: 16 bit signed integer corresponding with touch        delta, 1 of 240 (firmware R/W)

The integrator numerically adds its value to the cell error value toobtain an updated integrator value. The integrator (cellIntegrator) ismultiplied by the input value (cellIIRout). The product is scaled by aright shift 25 (i.e. divide by 33554432). This number is the gainadjusted cell value. An error value is created by subtracting it fromthe set-point of 16384. The error value is scaled by Ki and then drivesthe integrator. The Ki value controls the loop bandwidth. Larger Kivalues increase the bandwidth and correspondingly reduce the responsetime of the loop.

The delta output (cellDeltaOut) is computed by subtraction from theset-point and final scaling by a tabulated factor (cellDeltaCal). Thefinal processed normalized cell value is then used by navigationfirmware to track touch location and intensity.

The value of Ki is of key importance to the successful normalization ofcapacitor cells. The sign of the error causes the selection of twopossible gain values. Capacitor values above nominal (called anti-touch)must be quickly tracked out by k2. Capacitor values below nominal(normal touches) are more slowly tracked out by k1. In addition, thevalue of k1 depends on whether a touch is sensed. A touch sense (deltathreshold exceeded) changes k1 to a much lower value to slow down cellgain adjustment so that a touch is not tracked out by the loop. Thisvariable gain process permits all cells to look alike with touches notperturbing the necessary fine gain trim

FIG. 7 shows one method 400 for controlling a touchscreen systememploying automatic gain control. The method, which is carried out foreach individual cell, begins at step 305 by setting values for defaultgain, scaling factor, threshold for touch detection, and no-touch setpoint. At step 310, the loop gain is set to the default value. At step315, the filtered output signal from the cell is sampled. The methoddetermines at step 320 whether the cell output signal is larger than theset threshold. If the signal is larger than the threshold value,indicating that a true touch has occurred, the method goes to step 330at which a small value of the loop bandwidth factor Ki is chosen, but Ifthe signal S is smaller than the threshold value, indicating that notouch has occurred, the method goes to step 335 at which a large valueof the loop bandwidth factor Ki is chosen.

After either step 325 or step 330, the method continues on to step 335,where the Delta Output is calculated in terms of the scaling factor,no-touch set point, gain, and signal. Finally the value of gain isupdated at step 340 by the addition of the product of loop bandwidthfactor and the Delta Output and the method returns to step 315 to samplean individual cell signal.

Such a method allows the gain of each individual cell to be equalizedwith multiplicative adaptive correction, and also adaptively controlsloop bandwidth to facilitate tracking variations in cell gain whileignoring touch activity.

Note that much of the circuitry and many of the components, elements,devices and methods disclosed herein are employed in the AvagoTechnologies® AMRI-5200 touchscreen controller. A Preliminary ProductData Sheet for the AMRI-5200 touchscreen controller dated Apr. 20, 2011and entitled “AMRI-5200 Low-Power 10-Touch Controller,” filed on evendate herewith in a corresponding Information Disclosure Statement andcorresponding USPTO Form 1449, is hereby incorporated by referenceherein in its entirety.

Various embodiments are contemplated in addition to those disclosedhereinabove. The above-described embodiments should be considered asexamples, rather than as limiting the scope of the various embodiments.In addition to the foregoing embodiments, review of the detaileddescription and accompanying drawings will show that there are otherembodiments. Accordingly, many combinations, permutations, variationsand modifications of the foregoing embodiments not set forth explicitlyherein will nevertheless fall within the scope of the invention.

1. A capacitive touchscreen or touch panel system, comprising: atouchscreen comprising a first plurality of electrically conductivedrive electrodes arranged in rows or columns, and a second plurality ofelectrically conductive sense electrodes arranged in rows or columnsarranged at an angle with respect to the rows or columns of the firstplurality of electrodes, mutual capacitances existing between the firstand second pluralities of electrodes at locations where the first andsecond pluralities of electrodes intersect to form individual cells, themutual capacitances changing in the presence of one or more fingers of auser or touch devices brought into proximity thereto; drive circuitryoperably connected to the first plurality of drive electrodes; sensecircuitry operably connected to the second plurality of sense electrodesand configured to sense input signals corresponding to the individualcells therefrom, and a controller operably connected to the firstplurality of drive electrodes and the second plurality of senseelectrodes, the controller comprising a central processing unit (CPU)and automatic level control (ALC) circuitry comprising: at least onescaler and decimator circuit configured to receive signals correspondingto the individual cells and to provide therefrom scaled and decimatedoutput signals corresponding to such individual cells; a multipliercircuit operably connected to the scaler and decimator circuit andconfigured to receive the scaled and decimated output signals therefrom,and further to multiply such scaled and decimated output signals by again factor and to provide multiplier output signals therefrom; a firstsubtractor circuit operably connected to the multiplier circuit andconfigured to receive the multiplier output signals therefrom and tosubtract a predetermined set point value from such multiplier outputsignals thereby to provide error output signals therefrom; an ALCcontrol loop filter circuit operably connected to the CPU and themultiplier circuit and configured to calculate updated gain factorsbased on the error output signals and to provide such updated gainfactors to the multiplier circuit, and a second subtractor circuitconfigured to subtract multiplied output signals from a desired setpoint value and to provide final output signals corresponding thereto tothe CPU; wherein the CPU is configured to calculate touch position databased on the final output signals corresponding to the positions of theone or more fingers of the user or touch devices.
 2. The system of claim1, wherein the CPU is further configured to provide the touch positiondata to a host controller.
 3. The system of claim 1, wherein the ALCcontrol loop filter circuit comprises a shift register and anintegrator.
 4. The system of claim 1, wherein the ALC control loopfilter circuit is further configured to provide a gain factor that whenfed back to the multiplier minimizes the error signals.
 5. The system ofclaim 1, wherein the controller is configured to cause the ALC controlloop filter circuit to have a short time constant when no touch isdetected by the system.
 6. The system of claim 1, wherein the controlleris configured to cause the ALC control loop filter circuit to have along time constant when a touch is detected by the system.
 7. The systemof claim 6, wherein touch detection is determined by individual cellcapacitances dropping below a predetermined threshold.
 8. The system ofclaim 7, further comprising system firmware configured to determinetouch detection.
 9. The system of claim 1, wherein the controllercomprises ALC circuitry for each of N individual cells of thetouchscreen.
 10. The system of claim 1, wherein each of the N ALCcircuits uses the same predetermined set point value.
 11. The system ofclaim 1, wherein the signals corresponding to the individual cells aredigitized filtered output signals.
 12. The system of claim 1, whereinthe digitized filtered output signals have digital values rangingbetween about 5000 and
 50000. 13. The system of claim 1, wherein thepredetermined set point value ranges between about 16,000 and about20,000.
 14. A method of detecting touches on a capacitive touchscreen ortouch panel system, the system comprising a touchscreen comprising afirst plurality of electrically conductive drive electrodes arranged inrows or columns, and a second plurality of electrically conductive senseelectrodes arranged in rows or columns arranged at an angle with respectto the rows or columns of the first plurality of electrodes, mutualcapacitances existing between the first and second pluralities ofelectrodes at locations where the first and second pluralities ofelectrodes intersect to form individual cells, the mutual capacitanceschanging in the presence of one or more fingers of a user or touchdevices brought into proximity thereto, drive circuitry operablyconnected to the first plurality of drive electrodes, sense circuitryoperably connected to the second plurality of sense electrodes andconfigured to sense input signals corresponding to the individual cellstherefrom, and a controller operably connected to the first plurality ofdrive electrodes and the second plurality of sense electrodes, thecontroller comprising a central processing unit (CPU) and automaticlevel control (ALC) circuitry, the method comprising: scaling anddecimating signals corresponding to the individual cells to providescaled and decimated output signals corresponding to the individualcells; multiplying the scaled and decimated output signals by a gainfactor to provide multiplied output signals; subtracting the multipliedoutput signals from a predetermined set point value to provide erroroutput signals; calculating updated gain factors based on the erroroutput signals; subtracting multiplied output signals from a desired setpoint value and providing final output signals corresponding thereto,and calculating touch position data based on the final output signalsthat correspond to the positions of the one or more fingers of the useror touch devices.
 15. The method of claim 14, further comprisingproviding touch position data to a host controller.
 16. The method ofclaim 14, further comprising calculating and providing feedback gainfactors to minimize the error output signals.
 17. The method of claim14, further comprising detecting touches when individual cellcapacitances drop below a predetermined threshold.
 18. The method ofclaim 14, further comprising employing system firmware to detecttouches.